1. Field of the Invention
The present invention relates to a speech synthesizer.
2. Description of the Related Art
A speech uttered by a person has a speed variation according to contents of the speech uttered. This speed variation indicates where the speaker would emphasize. Further, this speed variation is associated with how much the hearer gets easy to hear. Accordingly, control of prosodemes of a speech speed, a volume, a pitch, etc is a technology necessary for generating the easy-to-hear synthetic speech.
Moreover, there is an instance in which almost the same sentences continue as in the case of a voice guidance, a weather forecast, etc. For example, there is a case of continuation of sentences vocalized by the speech synthesizer, such as [Today's weather in the Hokkaido region is fair.] ([kyou no Hokkaido chihou no tenki wa hare desu.]), [Today's weather in the Tohoku region is fair.] ([kyou no Tohoku chihou no tenki wa hare desu.]), [Today's weather in the Kanto region is cloudy.] ([kyou no Kanto chihou no tenki wa kumori desu.]), . . . [Today's weather in the Kyushu region is cloudy.] ([kyou no Kyushu chihou no tenki wa kumori desu.]). When the speech synthesizer vocalizes such sentences in a monotone, the hearer might feel a stress in some cases. Further, in the case of the speech in monotone, the hearer can not concentrate on a want-to-hear point in the speech and might fail to hear the want-to-hear point.
Patent document 1 (“Japanese Patent Application Laid-Open Publication No.9-160582”) discloses a speech synthesizing technology of controlling a speed of the synthetic speech by inserting a speed control symbol in between paragraph boundaries delimited as a result of analyzing a text as by a morphological analysis when desiring to change the speech speed.
Patent document 2 (“Japanese Patent Application Laid-Open Publication No.2000-75882”) discloses the speech synthesizing technology of controlling the speed of the synthetic speech by inserting (the speed control symbol) in between each mora (which are defined based on a unit as a plurality of speech syllables structuring character information) delimited as a result of analyzing the text as by the morphological analysis when desiring to change the speech speed.
Patent document 3 (“Japanese Patent Application Laid-Open Publication No.8-83095”) discloses a speech speed control technology based on changing a length of a silence interval between breath groups. This technology involves executing a process of expanding the silence interval, extending a pitch interval and repeating the pitch interval.
Further, Patent document 4 (“Japanese Patent Application Laid-Open Publication No.2000-267687”) discloses a technology of reading sentences in a way that skips the sentences exhibiting a low degree of importance.
A technology of Patent document 5 (“Japanese Patent Application Laid-Open Publication No.10-274999”) is that a keyword is extracted from a title and a summary in order to search for an important phrase in the sentence. Then, in this technology, it is judged whether or not the extracted keyword is contained in the sentence concerned. This technology involves controlling the speech speed etc to make an output speech distinguishable in accordance with a result of the judgment.
In the technologies of the Patent documents 1 and 2, the synthetic speech having a desired speed can be generated by inserting the speed control signals in between the group paragraphs and in between the each mora. In the technologies of the Patent documents 1 and 2, however, it is required that the speech speed control signal be manually changed for attaining the desired speech speed. Therefore, this operation needs manpower. Further, if an order of the sentences is not set beforehand in the speech synthesizer, a problem arises, wherein the speech speed can not be changed from time to time.
In the speech speed control technology (Patent document 3) of changing the length of the silence interval between the breath groups, it might happen that a result of the silence interval being short and a result of non-existence of the silence interval are outputted. Due to these drawbacks, such a problem occurs that prosodemes are disordered, and the hearer, when hearing such a synthetic speech, might hear like getting choked in breathing.
In the technology (the technology of Patent document 4) of controlling the speech utterance time by skipping (the sentences), the whole speech utterance time can be reduced. A problem is, however, such that this technology can not be applied to a case of having the necessity of reading all the sentences without any deletion as in the case of the sentences for the voice guidance.
In the speech speed control technology (the technology of Patent document 5) using the keyword, a problem is that the keyword does not invariably indicate the important phrase of the sentence to be read. For instance, in the example of the weather forecast described above, if the weather is the keyword, in a case where the same weather continues such as. [Today's weather in the Tohoku region is fair.] ([kyou no Tohoku chihou no tenki wa hare desu.]) and [Today's weather in the Kanto region is fair.] ([kyou no Kanto chihou no tenki wa hare desu.]), a different phrase (e.g., a date and a name of the region) might be more important to the hearer than the phrase corresponding to the weather. In the conventional technologies, however, the speech synthesizer changes the phrase corresponding to the keyword, and hence there arises such a problem that the speech speed of the phrase important to the hearer is not changed. Further, in this technology, the weather, the date and the name of the region are registered as the keywords, and, when the sentences containing these keywords are consecutively outputted as the speeches from the speech synthesizer, a problem is that there is no difference between the sentences outputted as the speeches. Hence, another problem of this technology arises, wherein the phrase desired most to be heard by the hearer can not be emphasized.